Thursday, May 14, 2009

"Selfish-Sperm" : Perfect Nemesis of Embryo Development.

.....Got hold of few papers that talk about Sperms which accumulate mutations as men age. Such mutations accumulate over time and offer a survival advantage to the sperm (hence, 'Selfish-Sperm'), but ultimately harm the offspring.

Most studies focus on the female germ line (oocytes), and very few studies have been able to examine directly mutations affecting the male germ line. Using techniques developed over the last seven years, Dr.Wilkie has attempted to answer just that.

The listed paper and several reports thereon point out that sperms accumulate mutations over time in several genes, but in some of them, notably, RET, FGFR2 and FGFR3, the rate at which errors are picked up is many times the normal rate of mutation in sperm.

The mutation in FGFR-2, on which the study focusses, causes several severe genetic disorders, including Apert-syndrome, which causes premature fusion of the skull bones and webbing of the fingers and toes. It occurs in around one in every 70,000 live births.

Sayf Dr. Wilkie "In around 80 cases of Apert syndrome and two related disorders, without exception the faulty gene has come from the healthy father."

On the basis of the data, the researchers conclude that the genetic mutation leading to Apert syndrome occurs rarely, but offers cells carrying it some growth advantage. One speculation is that the mutation affects the cell division cycle of the stem cells that give rise to sperm. Instead of producing equal numbers of sperms and stem cells to produce future sperm, they produce excess stem cells. These mutant cells, generating mutant sperm, gradually increase in number relative to its non-mutated, wild-type counterparts.

Largely since the mutation has no ill-effects in the testes, as men age the sperm-cells carrying the mutation become disproportionately common, increasing the likelihood that one will successfully fertilise an egg.

This is where the actual problem lies, as the paternally-contributed mutation severely impairs the ability of FGFR2 to function (which is absolutely critical) during development of the embryo.